Underpaid according to people with sense. For one, market forces do not dictate reality. They are an artificial construction WE created and WE are responsible for. If they result in someone's mistreatment we should see it as it is and not wave our hands and say "well, market forces". Perhaps the mistreatment is not obvious to you but it is obvious to plenty.

For another, the "market forces" aren't really market forces because there are too many other things involved because we don't live in a vacuum of perfect capitalism. There are things like collusion, there are things like threat of loss of shelter and health, etc., that corrupt it. Proper market forces would require extremely powerful and knowledgeable agents that can freely accept and reject products. We're nowhere near close such a reality.

For an obvious example of immoral effects of "market forces", see googamooga's post over here: https://news.ycombinator.com/item?id=12553936

If you don't see anything wrong there and your reaction is just "well, market forces..." I think you need to take a step back and think about what we humans are doing on this planet.